A ptiny pterosaur from the Late Cretaceous

Apologies for the title… Anyone who was with me on my last trip to Romania will remember the discussion of the potential for small pterosaurs in the Late Cretaceous, which rapidly turned into the search for “ptiny pterosaurs”. While I’ve always liked giant pterosaurs (who doesn’t think they are cool?!), I’ve recently become interested in the uncommon and fragmentary remains of small pterosaurs from the Late Cretaceous, animals that were previously thought not to exist. Imagine my excitement last year when I received an email from my friend and colleague Victoria Arbour asking if I wanted to take a look at some material that had been identified as pterosaurian from the Late Cretaceous of Hornby Island, British Columbia.

Victoria sent me some pictures, and I contacted another friend and colleague Mark Witton. We had the specimen sent to us in the UK so we could look at it, and we spent quite a bit of time debating the identification. As the specimen is small (the humerus is incomplete, estimated at 75 mm long when complete, and the vertebrae are just a few mm long), we knew that it was important to consider the specimen as a bird. We consulted some colleagues who worked on birds, and we (or mostly Mark) read up on Mesozoic birds, and we came to the conclusion that this specimen was indeed a pterosaur. One major reason for this is that the specimen includes a notarium, a feature consisting of fused vertebrae in the pectoral girdle, where the wing musculature attaches, allowing for stronger, more robust wings. This feature is not present in any Mesozoic birds, strongly supporting our pterosaurian ID, which we published today in the Royal Society journal Open Science.

Hornby Fig 2
The humerus of the small pterosaur from Hornby Island in dorsal (a, b), ventral (c, d), proximal (e, f), and distal (g, h) views.

Once we were confident it was a pterosaur, we were extremely surprised by the size. At 75 mm total length, the humerus corresponds to an animal with a wingspan of about 1.5m. This is corroborated by the size of the vertebrae. The specimen comes from the Campanian Northumberland Formation of Hornby Island, British Columbia, a marine formation with few terrestrial vertebrates. During the latest Cretaceous (Campanian-Maastrichtian), pterosaurs are well known for being massive. These animals include the largest animals to every fly, reaching wingspans of 10 or more metres. Small pterosaurs, however, were thought to be virtually non-existent at this time, leading some authors to suggest that birds outcompeted small pterosaurs, forcing them to occupy different niches by reaching giant sizes. At just 1.5m, this new one would have been more close to birds at that time.

Hornby Fig 6
Our ptiny pterosaur looks a more similarly-sized animal in the eye – ptiny pterosaur meet house cat. Image by Mark Witton.

So the next question was, is this a juvenile? In order to figure that out, we looked at the gross bone morphology. The bone texture was fibrous, suggesting a younger animal. However, the vertebrae were fused and the notarium fully fused, suggesting it wasn’t a young juvenile. We then were able to take a thin-section of the humerus in order to look at the bone tissues, which was more interesting. Unfortunately, the humerus isn’t the best bone to look at because of some strange aspects of bone growth, but we could still find a few important things. First of all, we have evidence of secondary bone growth and remodelling, which isn’t something that happens in very young animals. We also found that the outer layer had no large open vascular canals, again something that is found in young animals. But how old was it? Another feature that we had was a layer on the inner surface of the bone called an endosteal lamella. This is a feature that is laid down later in life, once the medullary cavity of the bone has stopped growing. In other pterosaurs, this indicates the animal is not still rapidly growing, and in azhdarchids, it’s thought to be deposited relatively later on, suggesting this animal was approaching full size.

So what’s the big deal? Well as I mentioned before, there have been suggestions that birds outcompeted small pterosaurs, forcing them into giant sizes to survive. But then where are the juvenile giant pterosaurs? Juvenile pterosaurs must have still existed, yet we don’t see those in the fossil record. And surely that would be a problem if they couldn’t compete with birds? This is not the only documented example of a small pterosaur from the latest Cretaceous. Some small vertebrae from the Dinosaur Park Formation of Alberta suggest there are smaller animals, while there are unconfirmed reports of smaller things coming out of Romania as well. The Dinosaur Park Formation, however, has a documented preservation bias against small-bodied animals. Pterosaurs are already poorly preserved due to their hollow bones, and if small animals are not preserved, then a small pterosaur would be even less likely to occur. It seems that the odds are stacked against us finding a small pterosaur at this time.

I’m sure there are more specimens of this size out there, and we urge people to look in their collections, particularly at Late Cretaceous bird material to see if we can find more of it. Keep your eyes open for tiny pterosaurs!

There are many people I’d like to thank related to this project, but in particular thanks to Victoria for including me in the project, and to Marji Johns from the Royal BC Museum for putting up with my hundreds of emails over the last year. Also thanks to Mark Witton for the awesome illustrations, would made this project more fun, and for helping me out!

Hornby azhdarchoid PR web res ©Mark Witton 2016
A possible life-reconstruction of our pterosaur during the Campanian, by Mark Witton.

Martin-Silverstone E, Witton MP, Arbour VM, and Currie PJ. 2016. A small azhdarchoid pterosaur from the latest Cretaceous, the age of flying giants. Royal Society Open Science 3: 160333.

Media links (from people we actually spoke with, there are more done from the press release):

National Geographic – Cat-sized flying reptile shakes up pterosaur family tree

Motherboard/VICE – Palaeontologists find a rare type of pterosaur near Vancouver Island

Nature News – Tiny pterosaur claims new perch on reptile family tree

IFLScience – This 77 million year old dwarf pterosaur was the same size as a cat

LiveScience – Teensy pterosaur was the same size as a house cat

The Conversation – Our new pterosaur fossil shows birds and small reptiles flew side by side

The Verge – This cat-sized pterosaur looks like adorable origami

Christian Science Monitor – Was this quirky animal the ptiniest pterosaur of the Late Cretaceous?


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